1. Field of the Invention
The invention is related to an electrical connector assembly which comprising a pick up cap being mounted to a electrical connector for providing a flat top surface to be engaged by a vacuum suction device.
2. Description of the Prior Art
At present, electronic components such as electrical connectors are mounted onto circuit substrates such as printed circuit boards (PCBs) by surface mount technology (SMT).
A method of mounting an electrical connector onto a PCB by SMT generally comprises a sequence of the following steps A through F:    A—Application of an adhesive film on the PCB having a plurality of metal contact pads. The application of the adhesive film may be performed by screen printing, pin transfer, or from a dispenser onto predetermined areas of the PCB.    B—Activation of the adhesive film by irradiation with actinic light in the ultraviolet (UV) or visible wavelength ranges between 200 and 600 nm, to a degree and for a period of time such that a desired initial tackiness is produced.    C—Mounting the connector with its contacts on the activated adhesive film and the metal contact pads of the PCB.    D—Curing the adhesive film at a temperature between 60˜140° C.; for example, in a convection cabinet, using infrared radiant heaters or by means of the actinic radiation source used in step B if such source also produces infrared radiation.    E—Producing electrical engagement between the contacts of the connector and the corresponding metal contact pads of the PCB by soldering in a wave solder machine or in drag soldering equipment.    F—Cooling the assembly to room temperature.
In step C, the connector is accurately positioned on the PCB by a vacuum suction device. Generally, a typical connector has a plurality of holes in a flat top portion thereof. Thus the connector does not have a suitably smooth, integral top surface for engagement by a vacuum suction device. Typically, a pick up cap is attached on the top portion of the connector to provide a required plane top surface.
U.S. Pat. No. 5,681,174, discloses a pick up cap adapted to be releasably secured to a board to board electrical connector assembly for positioning the assembly to a surface of an electrical article by using a vacuum suction device. The connector assembly includes a housing having a plurality of receiving holes for receiving contacts therein. The contacts are soldered onto the surface of the electrical article. The pick up cap, which overlies at least a central region of the housing, has a plate having planar surface and at least one projection extending substantially perpendicularly from a lower surface of the pick up cap intermediate the side edge thereof to retain the pick up cap on the connector assembly during positioning of the connector assembly to the electrical article. The dimension of the board to board connector is small, and the housing is in a shape of strip, thereby the dimension of the pick up cap is correspondingly small, and only few of the receiving holes of the housing are sheltered by the pick up cap. When curing the adhesive file at high temperature, heat air can flow quickly through the receiving holes to a bottom portion of the connector assembly and reliable electrical connection is subsequently produced between the contacts of the connector and the electrical article.
However, the aforecited pick up cap is not suitable to a land grid array (LGA) connector. Generally, the dimension of this connector is large, and in a shape of square, the dimension of the pick up cap is correspondingly large, the number of the receiving holes of the housing is correspondingly large, thereby a large number of receiving holes are sheltered by the pick up cap. When curing the adhesive film at high temperature in a convention cabinet using infrared radiant heaters, heat air can only flow through a few of the receiving holes which are not sheltered by the pick up cap to a bottom portion of the housing. Generally, the time needed for curing the adhesive film is short. Thus, the adhesive film is liable to cure non-uniformly. When this happens, electrical engagement between some of the contacts and the corresponding PCB may be flawed. The connector may not reliably electrically connect with the electrical article. Additionally, when cooling the entire assembly to room temperature, heat air can only be dissipated out through the receiving holes that are not sheltered by the pick up cap. This increase the time need for cooling the assembly, which reduces the efficiency of mounting the connector onto the PCB.
For solving the above-mentioned problem, another pick up cap is provided. The pick up cap has generally rectangular vents extending through the planar body in a vertical direction thereof. When curing the adhesive film at high temperature in a convention cabinet using infrared radiant heaters, heated air can flow through the vents and get to a bottom of the connector quickly. Therefore, the connector can be reliably electrically soldered onto the PCB in a short time, and the efficiency of mounting of the connector onto the PCB is improved. However a new problem appears because of the vents in the pick up cap, dirty material is liable to adhere to the contacts of the connector through the vents, which effects performance of the contacts.
In view of the above, a new pick up cap that overcomes the above-mentioned disadvantages is desired.